1. Field of the Invention
The present disclosure relates to an injection molding machine, and more particularly, to a toggle type injection molding machine.
2. Description of Related Art
An injection molding machine is used to produce molded products by injecting melted resin from an injection unit and filling the same in a cavity of a molding unit, followed by solidification. The molding unit is composed of a fixed mold and a moveable mold. Mold closing and mold opening of the molding unit is performed by a clamping unit. The clamping unit of the toggle type injection molding machine includes a moveable platen, a fixed platen, and a driving source such as a motor and a toggle link to move the moveable platen.
A general injection mode of the injection molding machine is as follows. First, the moveable platen of the clamping unit in mold open state is moved toward the fixed platen at a high speed. When the moveable mold installed on the moveable platen comes into contact with the fixed mold installed on the fixed platen as the moveable platen moves, the pressure increases to produce a clamp force. A nozzle of the injection unit is moved forward to the mold to inject resin, followed by cooling. Subsequently, the moveable platen of the clamping unit is moved backward to separate the moveable mold from the fixed mold, and finally, the moveable platen is moved backward quickly to eject an injection molded product.
In the toggle type injection molding machine, a detailed description of a process of applying the clamp force to the mold is provided as follows. First, after the toggle link becomes maximum unfolded state, a plate supporting the toggle link is moved forward until the moveable mold mounted on the moveable platen comes into contact with the fixed mold mounted on the fixed platen. In this state, the moveable platen is moved backward as much as a predetermined dimension. As a result, the toggle link becomes a folded state at a predetermined amount. Subsequently, the plate supporting the toggle link is moved forward as much as a predetermined dimension. Subsequently, in a state that the plate is stopped, when the toggle link is unfolded to the maximum, tie bars fixed to the plate and the fixed platen are stretched, and in this instance, a clamp force is generated by a restoration force of the tie bars.
Mold thickness control is to adjust the position of the moveable platen when generating the clamp force to the mold in the injection molding machine. As the toggle type injection molding machine is an injection molding machine using the toggle link of a link structure that expands and transmits a force, mold thickness is adjusted by position adjustment of the moveable platen and the plate used to support and move the toggle link. However, a motor with low precision, for example, a 3-phase induction motor, may be used as a motor used to adjust the position of the plate, and in this case, it is difficult to precisely adjust the position of the plate. For example, although the plate was moved forward 1 mm, the plate actually went further in some instances. Also, although a high precision motor is used, reduction ratios differ in each model of the injection molding machine, causing a difference in precision.